Heretofore, various types of display image observation devices have been conventionally known which display a desired image from an image display element, such as a liquid crystal display panel, and which enlarge the image using an eyepiece. An example of such an eyepiece used in a display image observation device is the eyepiece disclosed in Japanese Laid-Open Patent Application H6-308396. This eyepiece makes it possible to obtain a flat and clear image throughout the periphery of the field while using only a few lens elements by employing an aspherical surface and by making the object surface (i.e., the source image) a curved surface. However, this eyepiece is limited to cases where the range for favorably correcting the aberration designates an entrance pupil diameter of less than 4 mm (since the brightest lens disclosed has an F.sub.No. of 3.7).
The pupil diameter of most people is in the range from 3 to 4 mm and, when observing in a motionless environment, using a lens with an F.sub.No. of 3.7 gives satisfactory results. However, when the observation is accompanied by vibrations or other motion, such as while the observer is riding in an automobile or while walking, the entrance pupil of the eyepiece and the pupil of the observer can be temporarily offset as much as 3 to 5 mm due to the vibrations or other motion. Therefore, if the various aberrations are not favorably corrected for an entrance pupil of several tens of millimeters, then the viewed image will deteriorate to an inferior image quality as a result of the vibrations or other motions. This breakdown in the image quality causes favorable observation under such conditions to become difficult.